[coreboot] CBFS breaks relative payload paths

[Richard Smith]

Without CBFS a payload path like

payload ../../bios.vx855.090330.bin.elf

works.  This is nice because I don't lose my binaries everytime I blow 
away the work directory and keeps them in a location where copying (or 
tarballing) the trees around keeps the images with them.

If you try to build with CBFS then this fails.  Looks like the cbfstool 
runs in a directory that is one level above from 'image'.

I see a tools directory but cbfstool is not build there but rather one 
level up.

Seems reasonable to me that the build should copy the working files into 
the image directory and work with them from there.